Background: Calcifying pseudoneoplasm of the neuroaxis (CAPNON) is a very rare benign lesion that can be located anywhere in the nervous system, with only 59 intracranial cases described. The general lack of knowledge about this lesion hinders its preoperative diagnosis. Despite the consistent image findings, the final diagnosis is only established based on anatomopathological and immunohistochemical studies. The lesion is more commonly positive for epithelial membrane antigen (EMA) and vimentin, and negative for glial fibrillary acidic protein (GFAP) and S-100, suggesting a leptomeningeal origin. The opposite, however, may also occur, although very rarely (just two cases positive for GFAP and negative for EMA and vimentin reported this far). The treatment consists of total resection of the lesion, which yields a good prognosis. Case Presentation: We report the case of a 23-year-old female who presented with disperceptive focal seizures, sometimes evolving to bilateral tonic-clonic seizures, starting at age 9. She had a nodular calcified lesion in the left precuneus and inferior parietal lobe. The lesion was completely resected, and the immunohistochemical study revealed positivity for EMA, vimentin, GFAP, and S-100. No case hitherto published was positive for all four markers. This atypical immunohistochemical profile of the CAPNON may suggest a dual origin of this lesion, both parenchymal and leptomeningeal. Conclusion: The general lack of knowledge of CAPNON makes this lesion underdiagnosed. Therefore, in the face of a calcified lesion in the nervous system, one should consider the possibility of a CAPNON among the differential diagnoses. The immunohistochemistry is undoubtedly an important tool, but the anatomopathological study, associated with image findings, remain the gold standard for the diagnosis of CAPNON.

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OBJECTIVE One of the few resources for treating medically intractable pain is ablative surgery, but its indications have fallen dramatically over the last decades. One such procedure is mesencephalotomy. This study aims to determine current risks and benefits of MR-guided semidirect targeting–based stereotactic mesencephalotomy. METHODS This was a retrospective study based on a review of the medical records of 22 patients with nociceptive (n = 5), neuropathic (n = 10), or mixed (n = 7) refractory pain treated with unilateral mesencephalotomy alone (17 patients) or associated with bilateral anterior cingulotomy (5 patients) between 2014 and 2021 in the authors’ institutions. The confidence interval adopted in this study was 95%. RESULTS The sample included 12 women and 10 men with ages ranging from 23 to 80 years (mean 55.1 ± 17.1 years). Using MR-guided semidirect targeting, the following structures were targeted: spinoreticulothalamic (neuropathic/mixed pain, n = 17), trigeminothalamic (nociceptive/mixed pain in the face, n = 5), and neospinothalamic (nociceptive/mixed pain in the body, n = 7) pathways. The most common response to macrostimulation was central heat/moderate discomfort. Radiofrequency thermocoagulation was made with 70°C–75°C/60 sec. A total of 86.3% (3 months) and 76.9% (12 months) of the patients achieved excellent or good results (improvement of pain > 50%), presenting with a significant mean pain relief of 80.1% at 3 months and 71.4% at 12 months postoperatively. The addition of bilateral anterior cingulotomy did not improve the results. Patients with upper limb, cervicobrachial, and face pain did significantly better than those with trunk pain. The worst results were seen in patients with neuropathic and/or trunk pain. The surgical failure (pain relief ≤ 25%) and recurrence rates were 9.1% each, apparently related to the use of lower lesioning parameters (70°C/60 sec) and to the presence of neuropathic and/or trunk pain. The morbidity rate was 8%, with both complications (vertical diplopia and confusion/agitation) happening in patients lesioned with 75°C/60 sec. There were no deaths in this series. CONCLUSIONS These results show that contemporary stereotactic mesencephalotomy is an effective, relatively low-risk, and probably underused procedure for treating medically intractable pain. Careful semidirect determination of the target coordinates associated with close attention to electrical macrostimulation responses certainly plays an important role in avoiding complications in most of the procedures. A higher lesioning temperature (75°C) apparently prevents recurrence, but at the cost of an increased risk of complications.